(a) Field of the Invention
The present invention relates to a fuel feeding apparatus for internal combustion engines which comprises an area type air flow rate measuring section in which the air flow is dependent on the displacement of an air flow rate detecting valve, and a fuel flow rate measuring and distributing section in which a variable orifice defined by a rotor and a stator determines the fuel flow rate proportional to the air flow rate, said apparatus being characterized in that the air-fuel ratio is compensated by the output signal from an exhaust gas sensor disposed in the exhaust pipe.
(b) Description of the Prior Art
Various types of such fuel feeding apparatus have already been invented. An example thereof is shown in FIG. 1. In FIG. 1, the numeral 1 designates a fuel flow rate measuring and distributing section and 2 designates an area type air flow rate measuring section. The measuring and distributing section 1 comprises a stator 3 and a rotor 4. The stator 3 has a fuel inlet 5 and fuel outlets 6. The inlet 5 is formed with an annular groove 7, while each outlet is formed with an orifice 8. The rotor 4 has a fuel inlet 9 which is in constant communication with said inlet 5 through said annular groove 7, and a triangular window 10 which opens to an outlet 8. The rotor 4 is rotated in synchronism with an engine 12 through a shaft 11 and is axially slid as the flow rate detecting valve 15 of the area type air flow rate measuring section 2 is moved, as will be later described in more detail, thereby changing the time during which the triangular window 10 opens to the orifice 8. (See FIG. 2)
The area type air flow rate measuring section 2 comprises a servo-valve mechanism 16 adapted to sense the pressure difference (P1-P2) across a flow rate detecting valve 15 disposed upstream of a throttle valve 14 placed in a suction pipe 13 and maintain said pressure difference at a fixed value and amplify the same, and a valve opening mechanism 17 adapted to control the pressure difference (P1-P2) across the flow rate detecting valve 15 by using a pressure Pn amplified by the servo-valve mechanism 16. The servo-valve mechanism 16 comprises a chamber a subjected to a pressure P1, a chamber b subjected to a pressure P2, said chambers a and b being separated from each other by a diaphragm 18, a chamber c maintained at the same pressure as the pressure P1 in the chamber a, a variable orifice 20 whose area of opening is varied by a ball valve 19 fixed to the diaphragm 18, and a chamber d at a pressure Pn which is varied by the orifice 20 within the range of the pressure difference (P1-P2) between the chamber c and an intermediate chamber 21 (which is disposed between the flow rate detecting valve 15 and the throttle valve 14). The numeral 22 designates a bimetal disposed in the chamber a for controlling the diaphragm 18 so that the air-fuel ratio will be reduced, i.e., the amount of fuel in the mixed gas will be increased during the warm-up of the engine, the arrangement being such that when a heater 24 is energized through a switch 23, the bimetal 22 will be bent upward to release the diaphragm. The numeral 25 designates a pressure difference setting spring disposed in the chamber c, and 26 designates a bellows containing a gas at a reference temperature and a reference pressure, the effective area of said bellows 26 being determined so that (the effective area of the bellows 26).times.(the pressure of the reference gas)=(the effective area of the pressure difference setting diaphragm 18 of the servo-valve mechanism 16).times.(the difference pressure at the reference temperature and pressure). In addition, the bellows 26 is used to ensure that the area of opening of the flow rate detecting valve 16 will be proportional to the weight flow rate of air, and it is unnecessary if said area of opening is to be proportional to the volume flow rate of air.
The valve opening mechanism 17 causes the pressure Pn in the servo-valve mechanism 16 to act on a bellows 31 to control the axial position of the shaft 32 of the flow rate detecting valve so that the pressure difference P1-P2 across the flow rate detecting valve 15 will have a certain fixed value. The shaft 32 of the flow rate detecting valve controls the axial position of the rotor 4 of the fuel flow rate measuring and distributing section 1 so that the time of communication of a fuel metering port defined by the orifice 8 and triangular window 10 will be proportional to the weight flow rate of air. The numeral 33 designates a fuel tank; 34 designates a fuel pump; and 35 designates a pressure regulator. The pressure regulator 35 is divided into chambers e and f. The chamber e has installed therein a difference pressure setting spring 37 and an adjusting screw 38 and is subjected to a negative pressure P4 existing in the vicinity of an injector 39 at the suction pipe 13, while the chamber f has installed therein a valve seat 40 fixed to the diaphragm 36 and a valve 41, said valve seat 40 and valve 41 constituting a variable valve. The chamber f communicates with the fuel pump 34 and with the inlet 5 of the fuel flow rate measuring and distributing section 1, while the valve 41 communicates with the fuel tank 33. Therefore, the diaphragm 36 is subjected to the suction pipe negative pressure P4 in the vicinity of the injector 39 and to the feed pressure P3 at which the fuel is fed to the measuring and distributing section 1, so that it detects the pressure difference P3-P4. If the pressure P4 changes, the diaphragm 36 will be bent upward to increase the area of opening between the valve seat 40 and the valve 41, thus increasing the amount of fuel flowing from the valve 41 back to the fuel tank 33. As a result, the feed pressure P3 is reduced, and when a predetermined pressure difference is reached, the diaphragm 36 will be balanced and come to rest. In brief, the pressure regulator 35 maintains the pressure difference P3-P4 across the fuel metering and distributing section 1 at a fixed value irrespective of variations in the suction pipe negative pressure P4, thereby ensuring that the time of communication between the orifice 8 and the triangular window 10 will be uniquely proportional to the flow rate of fuel.
Because of the arrangement described above, the time of communication of the orifice is proportional to the area of opening of the flow rate detecting valve 15, as described above. As a result, the fuel flow rate is proportional to the weight flow rate of air, so that the air-fuel ratio is maintained at a constant value.